DE102019210019B4 - Optical apparatus for laser welding a workpiece, method for laser welding a workpiece by means of several partial beams and the use of optical apparatus for laser welding - Google Patents

Abstract

Optical apparatus (1) for laser welding a workpiece (2), comprising - a laser beam source (3) for providing a laser beam (4), - collimation optics (16) for collimating the laser beam (4) provided by the laser beam source (3), - a Beam splitter device (19) for splitting the collimated laser beam (18) into several partial beams (20a-20c), the beam splitter device (19) having a first setting device (26) with which the collimated laser beam (18) is split the multiple partial beams (20a-20c) is variably adjustable, and - a focusing optics (23) for focusing the partial beams (20a-20c) on the workpiece (2) to be welded, characterized in that the laser beam source (3) is a multiclad fiber (8) with a core fiber (9) and at least one ring fiber (10) and a second adjusting device (27), wherein with the second adjusting device (27) an input laser beam (6) at a first fiber end (7) of the Mul ticlad fiber (8) can be variably divided between the core fiber (9) and the at least one ring fiber (10), and a second fiber end (15) of the multiclad fiber (8) carries the laser beam (4) for the collimation optics (16) and that the beam splitter device (19) is designed to split the collimated laser beam (18) into at least two partial beams (20b, 20c) leading with respect to a specified welding direction (SR) and a trailing partial beam (20a), the leading partial beams Partial beams (20b, 20c) are lined up transversely to the intended welding direction (SR), and the energy distribution between the at least two leading partial beams (20b, 20c) on the one hand and the trailing partial beam (20a) on the other hand being carried out with the first setting device (26) can.

Description

• - eine Laserstrahlquelle zum Bereitstellen eines Laserstrahls,
• - eine Kollimationsoptik zum Kollimieren des bereitgestellten Laserstrahls der Laserstrahlquelle,
• - eine Strahlteiler-Einrichtung zum Aufteilen des kollimierten Laserstrahls auf mehrere Teilstrahlen, wobei die Strahlteiler-Einrichtung eine erste Einstellvorrichtung aufweist, mit der die Aufteilung des kollimierten Laserstrahls auf die mehreren Teilstrahlen variabel einstellbar ist, und
• - eine Fokussierungsoptik zum Fokussieren der Teilstrahlen auf das zu schweißende Werkstück.

The invention relates to an optical apparatus for laser welding a workpiece, comprising

• - a laser beam source for providing a laser beam,
• - a collimation optics for collimating the provided laser beam of the laser beam source,
• a beam splitter device for splitting the collimated laser beam into several partial beams, the beam splitter device having a first setting device with which the splitting of the collimated laser beam between the several partial beams can be variably adjusted, and
• - A focusing optics for focusing the partial beams on the workpiece to be welded.

Such an optical apparatus is from the DE 102 61 422 A1 known.

Using laser welding (also called laser beam welding), workpieces can be manufactured with a comparatively high welding speed (feed speed) and low thermal distortion.

When laser welding, the quality of the weld seam should also be ensured. During the welding process, undesirable spatter can form on the weld seam; Likewise, the weld seam produced can have undesirable waviness (“humping”) or undesirable edge notches and overall not achieve the desired mechanical strength. This usually limits the productivity (welding speed) during laser welding.

From the DE 102 61 422 A1 it has become known to split a laser beam for laser welding into two partial beams, one of the partial beams leading the other partial beam with respect to the welding direction. A laser beam is collimated and divided by means of a prism that can be moved transversely to the direction of the beam. One of the partial beams passes through a spot variation lens, and both partial beams pass through a focusing lens. This is intended to achieve welds of improved quality.

The splitting of a laser beam into several partial beams during laser welding is, for example, also based on the DE 10 2015 112 537 A1 , the WO 2018/099851 A1 who the DE 10 2016 105 214 A1 , the DE 10 2017 208 979 A1 or the US 2018/0185960 A1 known.

From the DE 10 2010 003 750 A1 it has become known to adjust the beam profile characteristics of a laser beam with a multiclad fiber. In particular, an original laser beam can be coupled with a first component into a core fiber and with a second component into a ring fiber surrounding the core fiber.

Multiclad fibers, for example, are also from the US 2002/0172485 A1 or the US 2006/0263024 A1 known.

The WO 2016/205805 A1 describes systems for laser welding in which several laser fibers can be used for several laser beams, and where diffractive optical elements are proposed for beam shaping.

If the laser welding is carried out as a through-weld, so that the material of the workpiece to be welded melts down to the underside of the workpiece, which is opposite the incident side of the laser beam, a good quality of the weld seam must be achieved with regard to both the upper side and the underside of the workpiece , for example with regard to spattering or waviness.

The post-published DE 10 2018 219 280 A1 describes a method for spatter-free casting, in particular with a solid-state laser, wherein in particular a first beam surface precedes a second beam surface, the first beam surface is larger than the second beam surface in terms of surface area and longer than the second beam surface, and a laser power belonging to the first beam surface is greater than a laser power belonging to the second beam area. The first beam surface can be divided into two partial beam surfaces.

WO 2019/130 043 A1 describes a method for butt welding two metal sheets, with two smaller laser spots each running in front of a larger laser spot in one of the metal sheets, with solid or liquid material always remaining between the associated vapor capillaries.

Object of the invention

It is the object of the invention to enable a good quality of weld seams at a higher feed rate, in particular for laser welding in penetration.

Description of the invention

This object is achieved according to the invention by an optical apparatus of the type mentioned at the outset, which is characterized in that
that the laser beam source comprises a multiclad fiber with a core fiber and at least one ring fiber and a second setting device, wherein with the second setting device an input laser beam at a first fiber end of the multiclad fiber can be variably divided between the core fiber and the at least one ring fiber, and wherein a the second fiber end of the multiclad fiber provides the laser beam for the collimation optics,
and that the beam splitter device is designed to split the collimated laser beam into at least two partial beams leading with respect to a intended welding direction and a trailing partial beam, the leading partial beams being lined up transversely to the intended welding direction,
and wherein the energy distribution between the at least two leading partial beams on the one hand and the trailing partial beam on the other hand can be adjusted with the first adjusting device.

According to the invention, laser welding can be operated with (at least) two leading (front) partial beams and one trailing (rear) partial beam. The energy distribution between the leading partial beams and the trailing partial beam can be set in a targeted manner with the first setting device. By using the multiclad fiber, a beam profile can be obtained on the workpiece to be welded with a core zone (from the core fiber) and at least one ring zone (from the at least one ring fiber) for the respective partial beams. The energy distribution between the core zone and the ring zone can be adjusted in a targeted manner by means of the second adjustment device. These degrees of freedom make it possible to optimize the laser welding process, in particular for laser welding in which the workpiece or the workpiece parts to be connected are welded through.

In the context of the invention, only one laser is required which generates the input laser beam, which is particularly simple structurally. With the optical apparatus, by means of the beam splitter device, (at least) three copies of the laser beam profiled by the multiclad fiber can be obtained.

In the context of the invention, the leading partial beams can be used to weld on the upper side of the workpiece. Due to the beam profile set up on the front partial beams by means of the multiclad fiber, particularly good quality can be achieved on the upper side of the seam. In particular, the laser power of the leading partial beams can be distributed across a comparatively large area or width by lining them up transversely to the feed direction (welding direction) and the beam profile. The penetration can be operated with the trailing partial jet. By preparing the workpiece by means of the preceding partial beams, a good seam quality can also be obtained on the underside of the workpiece.

In the context of the present invention, compared to laser welding with a simple leading partial beam and without setting up the beam profile according to the invention, a higher feed rate can be achieved without relevant humping or relevant notch formation (in particular on the upper side of the seam, but also on the underside) and without any relevant spatter formation (especially on the underside of the seam, but also on the upper side).

The multiclad fiber is typically designed as a 2in1 fiber, i.e. with a core fiber and exactly one ring fiber. Furthermore, the collimated laser beam is typically split into exactly two leading partial beams and one trailing partial beam.

The second adjustment device can, for example, shift the input laser beam relative to the first fiber end transversely to the direction of beam propagation, or also change the focusing of the input beam so that the width of the input beam at the first fiber end changes, cf. DE 10 2010 003 750 A1 .

The input laser beam is preferably generated by a solid-state laser.

Preferred Embodiments

An embodiment of the optical apparatus according to the invention is preferred which provides that the beam splitter device forms a deflection zone for each partial beam, and that with the first adjustment device the beam splitter device can be moved in at least one adjustment direction transversely to a beam propagation direction of the collimated laser beam, the Energy distribution between the partial beams can be adjusted via the overlap of the collimated laser beam with the respective deflection zones. Such beam splitter devices are structurally simple and also easy to use. The deflection zones each deflect a partial area of the cross-section of the collimated laser beam in a different direction than the other deflection zones (correspondingly, one deflection zone can allow the collimated laser beam to pass undeflected).

An advantageous further development of this embodiment provides that the deflection zones for the partial beams are arranged around a common center,
in particular where a deflection zone for the trailing partial beam occupies an angular interval of 180 ° around the common center,
and two deflection zones for exactly two leading partial beams each occupy 90 ° around the common center, and the adjustment direction runs along a border of the two deflection zones for the two leading partial beams. With this design, the leading partial beams can be evenly split into two partial beams in a simple manner, and at the same time a variable energy distribution occurs between the entirety of the leading partial beams on the one hand and the trailing partial beam on the other. The collimated laser beam aligned on the common center achieves a uniform distribution of the energy over the entirety of the leading partial beams on the one hand and the trailing partial beam on the other. The beam splitter device can be moved relative to the collimated laser beam along the direction of incidence onto the deflection zones for the leading partial beams in order to obtain an energy share greater than 50% for the leading partial beams, or it can be moved onto the deflection zone for the trailing partial beam in order to achieve a To obtain an energy share greater than 50% for the trailing partial beam.

An embodiment is preferred in which the beam splitter device is designed with a refractive optical element, in particular wherein the beam splitter device forms a wedge plate which has several deflection zones which form an inclination with respect to a beam propagation direction of the collimated laser beam and which form an inclination with respect to the beam propagation direction have different orientations. Such a beam splitter device is simple in construction and intuitive to use. It should be noted that a deflection zone of a wedge plate can also be formed without an inclination to the direction of beam propagation, or the wedge plate does not cover part of the cross section of the collimated X-ray beam in order to generate an undeflected partial beam.

In an alternative embodiment, the beam splitter device is designed with a diffractive optical element,
in particular wherein the beam splitter device has several diffraction zones which form sawtooth grids, the sawtooth grids having a different orientation with respect to a beam propagation direction of the collimated laser beam and / or having a different structure. The diffractive optical element is easy to manufacture and can be made comparatively compact. The sawtooth grid is formed by a surface of the beam splitter device as a height profile (thickness profile). It should be noted that a diffraction zone can also be formed without a sawtooth grating, or that the beam splitter device does not cover part of the cross section of the collimated X-ray beam in order to generate an undeflected partial beam. The diffraction zones (deflection zones) each deflect a partial area of the cross-section of the collimated laser beam in a different direction than the other diffraction zones.

Method according to the invention for laser welding

The scope of the present invention also includes a method for laser welding a workpiece,
whereby a workpiece is welded by means of several partial beams along one welding direction,
which is characterized by
that the workpiece is welded with at least two partial beams leading in relation to the welding direction and one trailing partial beam, the leading partial beams each having a beam profile with a core zone and at least one ring zone that lies around the core zone, the leading partial beams being lined up transversely to the welding direction,
and with the leading partial beams an integrated laser power in the respective core zone is greater than an integrated laser power in the respective at least one ring zone,
and that the leading partial beams produce a weld on the workpiece, and the trailing partial beam a weld through.

With the method according to the invention it is possible to weld a workpiece or its workpiece parts with a high seam quality both on the upper side of the workpiece and on the underside of the workpiece at a high feed rate (welding speed). In particular, the waviness (humping) and the formation of notches on the weld seam can be kept low (especially on the top, but also on the underside) and the formation of spatter can be kept low (especially on the underside, but also on the top).

Within the scope of the invention, with a respective (leading) partial beam, there is a greater integrated laser power on the core zone than on the at least one ring zone. The limited power input in the ring zone is advantageous for the quality of the weld seam on the upper side, in particular the weld pool dynamics can be low as a result. By means of the core zone, a sufficient welding depth can be guaranteed, also within the scope of the welding on the leading partial beam.

The power distribution between the core zone and the at least one (typically exactly one) ring zone can be selected specifically for a desired application. For example, in a partial beam, the integrated laser power in a respective core zone is at least 60%, preferably at least 65%, particularly preferably at least 70%, and in the respective at least one ring zone at a maximum of 40%, preferably a maximum of 35%, particularly preferably a maximum of 30% , in each case based on the total irradiated laser power of the partial beam.

Typically, the energy distribution between the leading partial beams (VT) and the trailing partial beam (NT) is between 40% VT / 60% NT and 60% VT / 40% NT.

A workpiece to be welded (or two partial workpieces of the workpiece to be welded) typically have a sheet thickness of 1 mm to 4 mm at the location of the weld.

The partial beams with the core zone and the ring zone generally have a two-stage top hat radiation profile. The laser intensity is essentially homogeneous within a respective ring zone, for example in a range of +/- 20%, preferably +/- 10% around an average value of the laser intensity in the ring zone; Likewise, the laser intensity within a respective core zone is essentially homogeneous, for example in a range of +/- 40%, preferably +/- 20% around an average value of the laser intensity within the core zone (here the transitions between core zone and ring zone and between ring zone and Surroundings / possibly further ring zones in which the laser intensity changes “abruptly”, but only a small part of the irradiated area, typically less than 15%, preferably less than 10%, compared to the neighboring core zone or ring zone turn off).

It is typically provided that a first setting device can be used to set an energy distribution between the leading partial beams on the one hand and the trailing partial beam on the other hand, and that a second setting device can be used to set an energy distribution between the respective ring zones and the respective core zones.

This can be used to change the energy distribution on a respective workpiece as the welding progresses, in order to optimize welding during various stages of the welding process, for example to make welding different from welding while the welding seam is being pierced by the laser beam operate. Likewise, the welding process can be optimized during the welding of a respective workpiece with a control loop with the setting devices, the welding being monitored with a sensor; for example, a specific (average) weld pool size and / or a specific (for example minimal) amplitude of a melt bath oscillation and / or a specific frequency of a melt bath oscillation can be adjusted.

Furthermore, workpieces of different workpiece types can be welded, the first setting device and the second setting device being set differently depending on the type of workpiece. For this, it is possible that for a workpiece type to be welded, different energy distributions between the at least two leading partial beams and the trailing partial beam as well as different energy distributions between the respective ring zones and the respective core zones are tried out in test welds and the quality of the weld obtained is assessed in each case, in particular under Inclusion of spatter formation during welding and the waviness and / or notch frequency of the weld seam obtained and taking into account the top and bottom, and that a set of optimal energy distributions for the workpiece type is determined on the basis of the test welds, in particular with a large number of workpieces of this workpiece type then is welded to the set of optimal energy distributions.

The method according to the invention can in particular run on an optical apparatus according to the invention described above.

Preferred process variants

In an advantageous variant of the method according to the invention for laser welding a workpiece, it is provided that the trailing partial beam also has a beam profile with a core zone and at least one ring zone which lies around the core zone. This makes it possible to generate the leading partial beams and the trailing partial beam in a simple manner from the same input laser beam that is subjected, for example, to beam shaping by means of a multiclad fiber. In addition, the quality of the underside of the seam can also be favorably influenced by this beam profile.

A further development of this variant is preferred, which provides that an input laser beam is fed into a first fiber end of a multiclad fiber with a core fiber and at least one ring fiber, whereby a laser beam is available at a second fiber end of the multiclad fiber is placed, from which a collimated laser beam is generated with collimation optics,
that the at least two leading partial beams and the trailing partial beam are generated from the collimated laser beam by means of a beam splitter device,
and that the partial beams are focused on the workpiece by means of focusing optics. As a result, the desired beam profile for the leading partial beam and also for the trailing partial beam with core zone and ring zone can be generated in a simple manner from just one input beam (and accordingly with just one laser).

In an advantageous variant, it is provided that on the workpiece the ring zones of the leading partial beams each overlap with the ring zone of the trailing partial beam, but not with the core zone of the trailing partial beam. Accordingly, the leading partial beams and the trailing partial beam as a whole form a coherent area on the workpiece that is illuminated by laser radiation. This reduces temperature gradients in the weld pool and thus reduces the melt pool dynamics.

In a preferred variant, it is provided that on the workpiece the ring zones of the leading partial beams overlap in the direction transverse to the welding direction between the core zones. At least the leading partial beams then form a coherent area on the workpiece that is illuminated by laser radiation. Temperature gradients transverse to the feed direction, in particular in the melt pool, can thereby be reduced, and the melt pool dynamics can be reduced overall.

In an advantageous further development of this variant, it is provided that the overlapping of the ring zones of the leading partial beams is set up so that the ring zone of the one leading partial beam extends essentially to the core zone of the other leading partial beam, but not with the core zone of the other leading partial beam overlaps. This further reduces temperature gradients in the weld pool and, in particular, avoids particularly high power input locally. The melt pool dynamics can be further reduced.

• 2*DK ≤ DR ≤ 5*DK,
• bevorzugt 2,5*DK ≤ DR ≤ 4,5*DK,
• besonders bevorzugt 3*DK ≤ DR ≤ 4*DK. Mit diesen Größenverhältnissen haben sich besonders gute Schweißnahtqualitäten ergeben. Die Laserenergie kann in den Ringzonen über eine ausreichende Fläche verteilt werden, und gleichzeitig können ausreichende Schweißtiefen erreicht werden, für die die Laserleistung in den Kernzonen von besonderer Bedeutung ist.

A variant is also preferred which provides that on the workpiece for one diameter DK a respective core zone and a diameter DR the following applies to each ring zone:

• 2 * DK ≤ DR ≤ 5 * DK,
• preferably 2.5 * DK ≤ DR ≤ 4.5 * DK,
• particularly preferably 3 * DK DR ≤ 4 * DK. With these proportions, particularly good weld seam qualities have resulted. The laser energy can be distributed over a sufficient area in the ring zones, and at the same time sufficient welding depths can be achieved, for which the laser power in the core zones is of particular importance.

• 200µm ≤ DK ≤ 600µm und 600µm ≤ DR ≤ 1500µm,
• bevorzugt 225µm ≤ DK ≤ 500µm und 750µm ≤ DR ≤ 1500µm,
• ganz besonders bevorzugt
• 250µm ≤ DK ≤ 400µm und 900µm ≤ DR ≤ 1500µm. Mit diesen Größenverhältnissen haben sich wiederum besonders gute Schweißnahtqualitäten ergeben, insbesondere bei zu schweißenden Blechdicken von 1 mm bis 4 mm.

A variant is also preferred in the case of the one on the workpiece for one diameter DK a respective core zone and a diameter DR the following applies to each ring zone:

• 200 µm ≤ DK ≤ 600 µm and 600 µm ≤ DR ≤ 1500 µm,
• preferably 225 µm ≤ DK ≤ 500 µm and 750 µm ≤ DR ≤ 1500 µm,
• especially preferred
• 250 µm ≤ DK ≤ 400 µm and 900 µm ≤ DR ≤ 1500 µm. With these size ratios, in turn, particularly good weld seam qualities have resulted, in particular in the case of sheet metal thicknesses of 1 mm to 4 mm to be welded.

The use of an optical apparatus according to the invention, described above, in a method according to the invention, described above, also falls within the scope of the invention. This enables laser welding with good weld seam quality and high productivity (feed speed), whereby the power distribution between the leading partial beams and the trailing partial beam as well as between the at least one ring zone / ring fiber and the core zone / core fiber can be flexibly adapted in order to optimize the laser welding process.

Further advantages of the invention emerge from the description and the drawing. The features mentioned above and below can also be used according to the invention individually or collectively in any combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather have an exemplary character for describing the invention.

Figure list

• 1 shows a schematic representation of an embodiment of an optical apparatus according to the invention;
• 2 shows a wedge plate designed beam splitter device for the invention in a schematic oblique view;
• 3 shows a schematic oblique view of a beam splitter device designed as a diffractive optical element for the invention and FIG a height diagram of the diffractive optical element;
• 4th shows schematically a focus image of a first variant of a method according to the invention for laser welding a workpiece, wherein the two leading partial beams and the trailing partial beam do not overlap;
• 5 shows schematically a focus image of a second variant of a method according to the invention for laser welding a workpiece, the leading partial beams not overlapping one another but with the trailing partial beam;
• 6th shows schematically a focus image of a third variant of a method according to the invention for laser welding a workpiece, the leading partial beams not overlapping one another but with the trailing partial beam;
• 7th shows a schematic diagram of the energy distribution in the beam profile of a leading partial beam for the invention;
• 8th shows a schematic diagram of the course of a refractive index of a multiclad fiber for the invention along a cross section.

The 1 shows an example of an optical apparatus according to the invention in a schematic representation 1 for laser welding a workpiece 2 . Note that the 1 left part of the optical apparatus 1 here enlarged compared to the right part of the apparatus for better understanding 1 is shown, and the enlargement transition in the area of the multiclad fiber 8th lies (see the dotted cone).

The optical apparatus 1 includes a laser beam source 3 for providing a laser beam 4th , which has a special beam profile, here with a core zone and a ring zone surrounding it.

For this, the laser beam source includes 3 here a solid-state laser 5 , the one here collimated input laser beam 6th provides. This input laser beam 6th is in a first (input-side) fiber end 7th a multiclad fiber 8th coupled. The multiclad fiber 8th shows a core fiber here 9 and a ring fiber surrounding it 10 on; it should be noted that in other embodiments one or more further ring fibers can be provided, which form the ring fiber 10 surround. Into the input laser beam 6th a wedge protrudes here 11 from one for the input laser beam 6th transparent but refractive material. This becomes a part 12th of the input laser beam 6th distracted. The distracted part 12th and an undistracted remaining part 13th of the input laser beam 6th are here through a focusing lens 14th on the first fiber end 7th focused, with the distracted part 12th into the ring fiber 10 and the undeflected, remaining part 13th into the core fiber 9 is coupled.

Over the length of the multiclad fiber 8th (which is shown in abbreviated form in the schematic representation) the laser power of the coupled parts is distributed 12th , 13th of the input laser beam 6th (depending on the laser modes and the length of the multiclad fiber) essentially uniformly over the entire cross-section of the core fiber 9 and ring fiber 10 . This is at a second (output) fiber end 15th the multiclad fiber 8th the laser beam 4th provided with a so-called two-stage top hat beam profile (see also below).

The one at the second fiber end 15th from the laser beam source 3 provided, profiled laser beam 4th is now with a collimation optics 16 collimated (parallelized). The collimation optics 16 is here with a collimating lens 17th educated; in other embodiments, for example, a combination of two crossed cylinder lens arrays can also be used. The collimated laser beam 18th is then by a beam splitter device 19th on at least three partial beams 20a , 20b divided, namely two leading partial beams and one trailing partial beam (in 1 not all partial beams are directly visible, see more below). The beam splitter device 19th is here as a wedge plate 21 formed the multiple deflection zones 22a , 22b has, which are formed differently inclined. The wedge plate 21 consists of for the laser beam 18th transparent but refractive material. The partial beams are accordingly 20a , 20b deflected in (slightly) different directions. The partial beams 20a , 20b are then by a focusing optics 23 the one here with a focusing lens 24 is formed on the workpiece 2 focused. The beam spots 25a , 25b of the partial beams 25a , 25b are due to the different deflection of the partial beams 20a , 20b at the beam splitter device 19th (slightly) shifted against each other. The beam spots 25a , 25b each point that through the laser beam source 3 and in particular the multiclad fiber there 8th impressed beam profile (see also the focus images below).

The wedge plate 21 is by a mechanism not shown, preferably a motorized mechanism, here along an adjustment direction HE and a second direction perpendicular to the plane of the drawing R2 movable; the direction of adjustment HE and the second direction R2 both run transversely to the direction of propagation AR of the collimated laser beam 18th and also perpendicular to each other. This allows the parts (energy parts) of the partial beams 20a , 20b that collimated from the laser beam 18th be obtained, changed. The wedge plate 21 or the beam splitter device 19th including the further mechanism, not shown, is accordingly used as the first adjustment device 26th denotes, with which a power distribution between the partial beams 20a , 20b , and in particular between the leading partial beams on the one hand and the trailing partial beams on the other hand, can be set.

The wedge 11 is by a further, not shown mechanism, preferably a motorized mechanism, along a first direction R1 that are transverse to the direction of propagation AR of the input laser beam 6th runs, movable. This allows the proportions (energy proportions) of the parts 12th and 13th of the input laser beam 6th to be changed. The wedge 11 including the mechanism not shown is accordingly used as a second adjustment device 27 denotes, with which a power distribution between the core fiber 9 (or the core zone of the beam profile) and the ring fiber 10 (or the ring zone of the beam profile) can be set.

The 2 shows schematically an exemplary wedge plate 21 , which in the context of the invention as a beam splitter device 19th for the collimated laser beam 18th (see. The dashed edge line) can be used.

The wedge plate 21 has three deflection zones here 31 , 32 , 33 on that around a center 34 are arranged around; the wedge plate 21 here has an essentially circular disk-shaped shape. The underside of the wedge plate 21 is here flat and perpendicular to the direction of propagation AR of the collimated laser beam 18th educated. At the top are the deflection zones 31 , 32 , 33 but with a different inclination or orientation compared to the direction of propagation AR educated.

The distraction zone 31 takes an angular interval of 180 ° around the center 34 a. The distraction zone 31 is aligned with the upper side perpendicular to the direction of propagation AR / z-direction (ie "without" inclination). The fraction of the collimated laser beam 18th that is on this distraction zone 31 hits, is due to an approximately perpendicular impact through the top of the wedge plate 21 not distracted. This portion forms the trailing partial beam. Note that the deflection zone 31 according to the invention can also be formed without material, that is to say the associated portion of the collimated laser beam 18th on the wedge plate 21 runs past ("half element", not shown in detail).

The distraction zone 32 takes an angular interval of 90 ° around the center 34 a. The top of the deflection zone 32 is opposite the top of the deflection zone 31 or opposite the plane perpendicular to the direction of propagation AR (= z-direction) of the collimated laser beam 18th slightly inclined, for example by -0.30 ° in relation to the x-direction and -0.12 ° in relation to the y-direction. The fraction of the collimated laser beam 18th pointing to the distraction zone 32 hits is distracted due to this tendency. This part forms a leading partial beam.

The distraction zone 33 also takes an angular interval of 90 ° around the center 34 a. The top of the deflection zone 33 is opposite the top of the deflection zone 31 or opposite the plane perpendicular to the direction of propagation AR (= z-direction) of the collimated laser beam 18th also slightly inclined, but mirror-symmetrical with regard to the xz-plane compared to the deflection zone 32 . The distraction zone 33 is inclined, for example, by + 0.30 ° relative to the x-direction and -0.12 ° relative to the y-direction. The fraction of the collimated laser beam 18th pointing to the distraction zone 33 hits is distracted due to this tendency. This portion forms a further leading partial beam.

In the relative position of the wedge plate shown 21 compared to the collimated laser beam 18th in which the collimated laser beam 18th on the center 34 the wedge plate 21 is centered, the two leading partial beams will each receive a power share of 25% and the trailing partial beam a power share of 50% of the total laser power.

The wedge plate can be used to change these performance components 21 from the shown centered position at least along the extension direction HE running along the border 35 of the two distraction zones 32 , 33 runs, be moved. The direction of extension HE runs parallel to the x-direction. By moving the wedge plate 21 (opposite the laser beam 18th ) In the positive x-direction, the power component of the trailing partial beam can be increased and the power component of the leading partial beam reduced, and vice versa.

Preferably the wedge plate 21 still from the position shown (and regardless of the displacement along the direction of extension HE ) also in the second direction R2 running along a border 36 between the deflection zone 31 and the distraction zones 32 , 33 runs, be moved. The second direction R2 runs parallel to the y-direction. By moving the wedge plate 21 (opposite the laser beam 18th ) in the positive y-direction the power component of the leading partial beam of the deflection zone 32 increased and the power component of the leading partial beam of the deflection zone 33 be decreased and vice versa; the power component of the trailing partial beam remains unchanged.

The different distraction effects of the distraction zones 31 , 32 , 33 the wedge plate 21 are based on the refraction of light, and accordingly is the wedge plate 21 as a refractive optical element 37 viewed.

Alternatively, it is also possible to use a beam splitter device 19th with a diffractive optical element 40 to train, see the schematic, exemplary representation in 3 For this. The diffractive, optical element 40 is made of one for the laser beam 18th made of transparent but refractive material; it in turn has a flat underside that is perpendicular to the direction of propagation AR lies. The diffractive optical element 40 also forms deflection zones 31 , 32 , 33 from the partial beams from the collimated laser beam directed in different directions 18th produce. The different distraction effects of the distraction zones 31 , 32 , 33 but are essentially based on diffraction of the collimated laser beam 18th , which is why the deflection zones 31 , 32 , 33 also as diffraction zones 41 , 42 , 43 are designated.

In the flexion zone 41 becomes in the embodiment shown the laser beam 18th not distracted because the diffractive optical element is there 40 flat on its upper side (with constant local height H , so without a sawtooth grid) is formed. Note that the diffraction zone 41 according to the invention can also be formed without material, that is to say the associated portion of the collimated laser beam 18th on the diffractive optical element 40 runs past ("half element", not shown in detail).

In the flexion zone 42 on the other hand, a sawtooth grid with a locally variable height (or locally variable thickness of the diffractive optical element) is at the top 40 in the direction of beam propagation AR ) of the diffractive optical element 40 set up, see the height profile below, in which the local height H (in the z-direction) against the location along the cutting direction a (see the dashed section plane A. ) is applied. With the diffractive optical element 40 is in the flexion zone 42 indicated with lines where the local altitude H each is equal and maximum. These lines are slightly inclined in relation to the y-direction (here by approx. + 15 °), which results in a corresponding slight deflection of the laser beam 18th in the area of the flexion zone 42 is achieved. The lines run perpendicular to the cutting direction shown a , and the sawtooth profile falls again and again along this cutting line and rises again and again abruptly.

The flexion zone 43 likewise has a sawtooth profile. With its lines, which indicate the same and maximum local height, this is opposite to the diffraction zone in relation to the y-direction 42 inclined, here with its lines by approx. -15 ° in relation to the y-direction, as a result of which there is a corresponding slight deflection of the laser beam in opposite directions 18th is produced.

Incidentally, the mode of operation of the beam splitter device 19th of 3 analogous to the beam splitter device from 2 .

In the 4th to 6th are shown schematically exemplary focus images that can be used within the scope of the invention. The focus images show the partial beams 20a-20c , which are directed to the top of the workpiece during laser beam welding and are focused on the workpiece or its surface by means of the focusing optics, at the location of the surface that corresponds to the plane of the drawing.

In the variants shown, with respect to a given relative welding direction (feed direction) SR two leading partial beams 20b , 20c and a trailing partial beam 20a used. The leading partial beams 20b , 20c are with respect to a transverse direction QR arranged in a straight line; the transverse direction QR runs perpendicular to the welding direction SR .

Typically all partial beams 20a , 20b , 20c generated from the same input laser beam that has received a special beam profile by passing through a multiclad fiber; this beam profile then also have all partial beams accordingly 20a , 20b , 20c on. The beam profile here includes a core zone 50 , within which there is an essentially constant power density LDK (“intensity”) of laser radiation, and a ring zone 51 , in which there is also an essentially constant power density LDR of laser radiation; in other variants, further ring zones can be provided.

The partial beams 20a , 20b , 20c basically pass through the same optical elements (in particular the focusing optics) after the beam splitter arrangement, so that the partial beams 20a , 20b , 20c have the same size on the workpiece. On the workpiece (or on the top of the workpiece), the diameter DK the core zone 50 and DR the ring zone 51 be measured. Mostly lies DK between 200 µm and 600 µm, often around 300 µm. Furthermore lies mostly DR between 600 µm and 1800 µm, often around 700 µm.

By means of a first adjustment device (cf. 1 ) can be used for all partial beams 20a-20c Laser power between the core zone 50 and the ring zone 51 be redistributed; those over the area of the core zone 50 integrated laser power ILK ("Integrated intensity") is greater than that over the area the ring zone 51 integrated laser power ILR , usually applies ILK : ILR≥60: 40 or even ILK : ILR≥70: 30. For the relationship DR / DK usually 2≤DR / DK≤5, mostly with 3≤DR / DK≤4.

By means of the second adjustment device (cf. 1 ) can laser power between the totality of the leading partial beams 20b , 20c on the one hand and the trailing partial beam 20a on the other hand be redistributed; the laser power VT integrated over the area of all leading partial beams 20ba, 20c and that over the area of the trailing partial beam 20a integrated laser power NT is typically approximately the same size; usually the following applies: VT: NT≤60: 40 and VT: NT≥40: 60.

With the leading partial beams 20b , 20c the workpiece is melted from the top, with the partial beams running in front 20b , 20c The weld pool area generated does not extend to the underside of the workpiece ("weld-in"). With the trailing partial jet, a weld pool area is created that extends to the underside of the workpiece ("penetration"). By combining the leading partial beams 20b , 20c with the trailing partial beam 20a it is possible to obtain a particularly high quality, in particular mechanically very strong, low-wave and low-notch weld seam with only little spatter formation during the welding process on the upper side and the lower side of the workpiece. The welding process can be optimized by adjusting the power distribution.

The 4th shows a variant in which the two leading partial beams 20b , 20c do not overlap with each other, and furthermore also the leading partial beams 20b , 20c not with the trailing partial beam 20a overlap. Note, however, that here in the welding direction SR the ring zone 51 of the approaching partial beam 20a regarding the welding direction SR up between the ring zones 51 of the leading partial beams 20b , 20c reaches out.

In this variant, the addition of laser power from different partial beams is avoided. This can help to keep the melt pool dynamics low and, in particular, to avoid spatter formation, especially on the upper side of the workpiece. This variant is often preferred for smaller workpiece thicknesses, for example between 1 mm and 2.5 mm workpiece thickness.

The 5 shows a variant in which the leading partial beams 20b , 20c again do not overlap. The leading partial beams 20b , 20c but overlap here in the overlap zones 52 with the trailing partial beam 20a in the area of the ring zones 51 ; the centers of the partial rays 20a , 20b and 20a , 20c but are so far apart that each between the overlap zone 52 and the two core zones 50 of the partial beams 20a , 20b and 20a , 20c still remaining areas 55 of non-overlapped ring zone 51 remain.

In this variant, the totality of the partial beams forms a coherent area illuminated by laser radiation. This can help to reduce temperature gradients in the weld pool and to reduce the waviness of the weld seam obtained or the formation of notches. This variant is often preferred for medium workpiece thicknesses, for example between 2.5 mm and 3.2 mm workpiece thickness.

The 6th shows a variant in which the leading partial beams 20b , 20c in the transverse direction QR in the area of the ring zones 51 overlap, but not with respect to the core zones 50 , see the overlap zone 53 . In the variant shown, the overlap zone is sufficient 53 but each to the core zones 50 touching. Furthermore, the leading partial beams overlap 20b , 20c with the trailing partial beam 20a in the area of the ring zones 51 . This creates areas of overlap 52 of the partial beams 20a , 20b and 20a , 20c preserved, but not up to the core zones here 51 approach; also exists in the overlap zone 54 here an overlap of the ring zones 51 of all three partial beams 20a , 20b , 20c .

In this variant, by adding the laser power of two partial beams over comparatively large areas and in the overlapping area 54 A locally increased power density of the laser radiation can even be achieved by three partial beams. As a result, greater penetration into the workpiece can be achieved, in particular in the overlap area of the two leading partial beams. This facilitates welding through with the trailing partial beam and, in particular, makes it accessible even at higher welding speeds and / or with a greater workpiece thickness. This variant is often preferred for larger workpiece thicknesses, for example between 3.2 mm and 4 mm workpiece thickness.

The 7th illustrates the intensity profile as an example 60 of a leading partial beam which can be applied to a workpiece as part of a method according to the invention. As a rule, a corresponding intensity profile is also given for the trailing partial beam on the workpiece. The intensity is applied upwards I. (Laser power per area) as a function of location x , where the x-axis runs through the center of the laser beam (at x = 0).

The intensity profile 60 here is a two-stage TopHat radiation profile; it can through use a double clad fiber (see 8th ).

The intensity profile 60 has a core zone 50 within which there is a high, essentially constant intensity I1 of here approx. 2.1 W / cm ² ; typically the intensity fluctuates in the core zone 50 by a maximum of 40%, preferably a maximum of 20%, around the mean intensity of the core zone 50 . The core zone 50 is surrounded by a ring zone 51 , within which there is a lower, likewise essentially constant intensity I2 of here approx. 0.4 W / cm ² ; typically the intensity fluctuates in the ring zone 51 by a maximum of 20% around the mean intensity of the ring zone 51 . In a transition area 61 from the core zone 50 to the ring zone 51 the intensity drops sharply; the intensity there can also drop below I2. In another transition area 62 from the ring zone 51 towards the external environment the intensity also drops sharply, here (in the absence of another core zone) to zero. The transition areas 61 , 62 typically make only small widths B1, B2 compared to the diameter DK the core zone 50 or to the width BR of the ring zone 51 for example with B1≤0.3 * \ DK or B1≤50.2 * DK, or with B2≤0.3 * BR or B2≤0.2 * BR.

The 8th illustrates an example of the structure of a multiclad fiber in a schematic diagram 8th in the area of core fiber 9 and ring fiber 10 ("Double clad fiber" or 2in1 fiber) for the invention; Note that a multiclad fiber with even more ring fibers can be used as an alternative. To the right is the place x in the cross section of the Multiclad fiber 8th applied, and upwards the refractive index n (for the wavelength used by the laser); at x = 0 is the center of the multiclad fiber 8th .

Inside the core fiber 9 and within the ring fiber 10 a light guide material with a high, here uniform refractive index nKR is arranged. Between the core fiber 9 and the ring fiber 10 a first cladding 70 made of a first cladding material with a refractive index nM1 is arranged. NM1 is significantly smaller than nKR; This creates a total reflection of the laser radiation into the core fiber 9 and the ring fiber 10 is coupled, on the first coat 70 reached. To the ring fiber 10 A second cladding 71 made of a second cladding material with a refractive index nM2 is arranged around it. In this case, nM2 is again significantly smaller than nKR in order to also apply to the second coat 71 to cause a total reflection of the laser radiation. In the variant shown, nM1 is also slightly less than nM2.

In the embodiment shown, the (outer) radius of the core fiber is 9 approx. 50 µm, and the outer radius of the ring fiber 10 approx. 300 µm.

List of reference symbols

1

optical apparatus

2

workpiece

3

Laser beam source

4th

Laser beam (provided by the laser beam source)

5

laser

6th

Input laser beam (provided by the laser)

7th

first fiber end

8th

Multiclad fiber

9

Core fiber

10

Ring fiber

11

wedge

12th

deflected part (of the input laser beam)

13th

undeflected part (of the input laser beam)

14th

Focusing lens

15th

second fiber end

16

Collimation optics

17th

Collimation lens

18th

collimated laser beam

19th

Beam splitter device

20a

(trailing) partial beam

20b

(leading) partial beam

20c

(leading) partial beam

21

Wedge plate

22a

Distraction zone

22b

Distraction zone

23

Focusing optics

24

Focusing lens

25a

Beam spot

25b

Beam spot

26th

first adjustment device

27

second adjustment device

31

Deflection zone (trailing partial beam)

32

Deflection zone (leading partial beam)

33

Deflection zone (leading partial beam)

34

Center (beam splitter device)

35

border

36

border

37

refractive optical element

40

diffractive optical element

41

Diffraction zone (trailing partial beam)

42

Diffraction zone (leading partial beam)

43

Diffraction zone (leading partial beam)

50

Core zone

51

Ring zone

52

Overlap zone (leading / trailing partial beam)

53

Overlap zone (leading / leading partial beam)

54

Overlap zone (three partial beams)

55

Residual area (of the ring zone without overlap)

60

Intensity profile

61

Transition area

62

Transition area

70

first coat

71

second coat

A.

Cutting plane

a

Section direction (in the diffractive optical element)

AR

Direction of propagation / direction of beam propagation

DK

Core zone diameter

DR

Diameter of the ring zone

HE

Direction of adjustment

H

local altitude

I.

intensity

ILK

integrated laser power core zone

ILR

integrated laser power ring zone

n

Refractive index

QR

Transverse direction

R1

first direction

R2

second direction

SR

Welding direction

x, y, z

Location coordinates

Claims (17)

Optical apparatus (1) for laser welding a workpiece (2), comprising - a laser beam source (3) for providing a laser beam (4), - collimation optics (16) for collimating the laser beam (4) provided by the laser beam source (3), - a Beam splitter device (19) for splitting the collimated laser beam (18) into several partial beams (20a-20c), the beam splitter device (19) having a first setting device (26) with which the collimated laser beam (18) is split the multiple partial beams (20a-20c) is variably adjustable, and - a focusing optics (23) for focusing the partial beams (20a-20c) on the workpiece (2) to be welded, characterized in that the laser beam source (3) is a multiclad fiber (8) with a core fiber (9) and at least one ring fiber (10) and a second adjustment device (27), wherein with the second adjustment device (27) an input laser beam (6) at a first fiber end (7) d he multiclad fiber (8) can be variably divided between the core fiber (9) and the at least one ring fiber (10), and a second fiber end (15) of the multiclad fiber (8) carries the laser beam (4) for the collimation optics (16 ) and that the beam splitter device (19) is designed to split the collimated laser beam (18) into at least two partial beams (20b, 20c) leading with respect to an intended welding direction (SR) and a trailing partial beam (20a), the leading partial beams (20b, 20c) are lined up transversely to the intended welding direction (SR), and the first setting device (26) is used to adjust the energy distribution between the at least two leading partial beams (20b, 20c) on the one hand and the trailing partial beam (20a) on the other can be done. Optical apparatus (1) according to Claim 1 , characterized in that the beam splitter device (19) forms a deflection zone (22a-22b; 31, 32, 33) for each partial beam (20a-20c), and that the beam splitter device (19 ) can be moved in at least one setting direction (ER, R2) transversely to a beam propagation direction (AR) of the collimated laser beam (6), the energy distribution between the partial beams (20a-20c) via the overlap of the collimated laser beam (18) with the respective Deflection zones (22a-22b; 31, 32, 33) can be set. Optical apparatus (1) according to Claim 2 , characterized in that the deflection zones (22a-22b; 31, 32, 33) for the partial beams (20-20c) are arranged around a common center (34), Optical apparatus according to Claim 3 , characterized in that a deflection zone (31) for the trailing partial beam (20a) occupies an angular interval of 180 ° around the common center (34), and two deflection zones (32, 33) for exactly two leading partial beams (20b, 20c) each 90 ° around the common center (34), and the adjustment direction (ER) runs along a border (35) of the two deflection zones (32, 33) for the two leading partial beams (20b, 20c). Optical apparatus (1) according to one of the Claims 1 to 4th , characterized in that the beam splitter device (19) is designed with a refractive optical element (37). Optical apparatus according to Claim 5 , characterized in that the beam splitter device (19) forms a wedge plate (21) which has several deflection zones (22a-22b; 31, 32, 33) which are inclined with respect to a beam propagation direction (AR) of the collimated laser beam (18) and which have a different orientation with respect to the direction of beam propagation (AR). Optical apparatus (1) according to one of the Claims 1 to 4th , characterized in that the beam splitter device (19) is formed with a diffractive optical element (40). Optical apparatus according to Claim 7 , characterized in that the beam splitter device (19) has several diffraction zones (41, 42, 43) which form sawtooth grids, the sawtooth grids having a different orientation with respect to a beam propagation direction (AR) of the collimated laser beam (18) and / or a have different structure. Method for laser welding a workpiece (2), wherein a workpiece (2) is welded by means of several partial beams (20a-20c) along one welding direction (SR), characterized in that the workpiece (2) is welded with at least two with respect to the welding direction (SR) leading partial beams (20b, 20c) and a trailing partial beam (20a) is welded, the leading partial beams (20b, 20c) each having a beam profile with a core zone (50) and at least one ring zone (51) surrounding the core zone (50 ), whereby the leading partial beams (20b-20c) are lined up transversely to the welding direction (SR), and with the leading partial beams (20b-20c) an integrated laser power (ILK) in the respective core zone (50) is greater than an integrated one Laser power (ILR) in the respective at least one ring zone (51), and that the leading partial beams (20b-20c) produce a weld on the workpiece (2), and the trailing partial beam ( 20a) a weld through. Procedure according to Claim 9 , characterized in that the trailing partial beam (20a) also has a beam profile with a core zone (50) and at least one ring zone (51) which lies around the core zone (50). Procedure according to Claim 10 , characterized in that an input laser beam (6) is fed into a first fiber end (7) of a multiclad fiber (8) with a core fiber (9) and at least one ring fiber (10), whereby the multiclad at a second fiber end (15) -Fiber (8) a laser beam (4) is made available, from which a collimated laser beam (18) is generated with collimating optics (16) that by means of a beam splitter device (19) from the collimated laser beam (18) the at least two leading partial beams (20b, 20c) and the trailing partial beam (20a) are generated, and that the partial beams (20a-20c) are focused on the workpiece (2) by means of focusing optics (23). Method according to one of the Claims 10 or 11 , characterized in that on the workpiece (2) the annular zones (51) of the leading partial beams (20b, 20c) each overlap with the annular zone (51) of the trailing partial beam (20a), but not with the core zone (50) of the trailing partial beam ( 20a). Method according to one of the Claims 9 to 12th , characterized in that on the workpiece (2) the ring zones (51) of the leading partial beams (20b, 20c) overlap in the direction (QR) transverse to the welding direction (SR) between the core zones (50). Procedure according to Claim 13 , characterized in that the overlap of the ring zones (51) of the leading partial beams (20b, 20c) is set up in such a way that the ring zone (51) of the respective leading partial beam (20b, 20c) essentially extends to the core zone (50) of the each other leading partial beam (20b, 20c) is sufficient, however, it does not overlap with the core zone (50) of the respective other leading partial beam (20b, 20c). Method according to one of the Claims 9 to 14th , characterized in that the following applies on the workpiece (2) for a diameter DK of a respective core zone (50) and a diameter DR of a respective annular zone (51): 2 * DK DR 5 * DK. Method according to one of the Claims 9 to 15th , characterized in that the following applies on the workpiece (2) for a diameter DK of a respective core zone (50) and a diameter DR of a respective annular zone (51): 200 µm DK 600 µm and 600 µm DR 1800 µm. Use of an optical apparatus (1) according to one of the Claims 1 to 8th in a method according to one of the Claims 9 to 16 .

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